JP2010135512A - Resistance change memory device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resistance change memory device which uses a spin transfer effect which reduces the transition probability into a quasi-stable state, and achieves the stable flux reversal over a wide range of an injection current to write in data. <P>SOLUTION: The memory device has a laminate of tunnel magneto-resistance effect elements 1 which include a memory layer 16 which can reverse a direction of memory layer magnetization 53 inside a resistance change type memory cell MC, and include magnetic layers 12, 14, and 16 formed on a connection plug 31, and a line connecting the center of each layer of the laminate is inclined diagonally from a direction vertical to an upper face of the connection plug 31 in which the laminate concerned is formed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a resistance change type memory device that writes data using a spin transfer effect by current injection.

  With the rapid spread of data communication devices, especially personal small devices such as mobile terminals, the elements such as memory and logic that compose this device have higher performance such as higher integration, higher speed, and lower power consumption. Is required. In particular, the nonvolatile memory is considered as an indispensable component for enhancing the functionality of the device.

As the nonvolatile memory, semiconductor flash memory, FeRAM (ferroelectric nonvolatile memory), and the like have been put into practical use. At present, active research and development is underway for further enhancement of performance.
Recently, MRAM (Magnetic Random Access Memory) using a tunnel magnetoresistive effect has been remarkably developed as a new nonvolatile memory using a magnetic material, and has attracted attention (for example, see Non-Patent Document 1).

Here, the operation principle of the MRAM that is closely related to the present invention will be briefly described.
The MRAM is a magnetic data recording element having a structure in which minute memory carriers made of a magnetic material are regularly arranged and wirings are provided so as to be accessible to each of them.
When a current is passed through both the lead (word line) and the read lead (bit line) arranged above or below the magnetic storage carrier, a combined current magnetic field is generated. Data writing to the MRAM is performed by controlling the magnetization of each magnetic material by a synthetic electromagnetic field.
In general, “0” data and “1” data are stored according to the direction of magnetization. As a typical method for rewriting element data, there is a method using asteroid characteristics (see, for example, Patent Document 1). There is also a method using switching characteristics (see, for example, Patent Document 2).

For data reading, cell selection is performed using an element such as a transistor, and the direction of magnetization is extracted as a voltage signal through the galvanomagnetic effect.
A structure including a three-layer junction of ferromagnetic material / insulator / ferromagnet (ferromagnetic tunnel junction, Magnetic Tunnel Junction-MTJ) has been proposed as a film structure of the cell. Hereinafter, this structure is referred to as an MTJ structure.
In the MTJ structure, one ferromagnetic layer is used as a fixed reference layer whose magnetization direction is fixed, and the other is used as a recording layer (free layer). Thus, the MTJ structure associates the recording layer magnetization direction with the voltage signal through the tunnel magnetoresistance effect.

The MRAM can rewrite data “0” and “1” due to magnetization reversal of a magnetic material at high speed and almost infinitely (10 15 times or more). This is the greatest feature of the MRAM when compared with other nonvolatile memories.
On the other hand, the MRAM consumes a large amount of power because a current of several [mA] to several tens [mA] flows through the wiring. In addition, since MRAM requires both a word line for recording and a bit line for reading, it is difficult to miniaturize cells. Furthermore, MRAM is disadvantageous for scaling from the viewpoint of power consumption because the magnetic field required for inversion increases when MTJ is reduced.

  As one of the solutions, a recording method that does not rely on a current magnetic field has been studied, and in particular, research on spin transfer magnetization reversal is active (see, for example, Patent Document 3).

The spin transfer magnetization reversal storage element is composed of MTJ as in MRAM. However, spin transfer magnetization reversal utilizes the fact that spin-polarized electrons passing through a magnetic layer fixed in a certain direction give torque to the magnetic layer when entering the free layer. Specifically, the free layer magnetization is reversed when a current exceeding a certain threshold value is passed.
Data rewrite of “0” and “1” is performed by changing the polarity of the current.
The absolute value of the current for this inversion is several [mA] or less for an element having a scale of about 0.1 [μm], and decreases in proportion to the element volume. In this respect, the spin transfer magnetization reversal storage element is advantageous in terms of scaling.
In addition, the spin transfer magnetization reversal storage element has an advantage that the cell becomes simple because a word line for recording required in the MRAM is unnecessary.

Reading uses the tunnel magnetoresistive effect as in MRAM.
In this specification, an MRAM using spin transfer is referred to as SpRAM (Spin transfer Random Access Memory). A spin-polarized electron current that causes spin transfer is called a spin injection current.
There is great expectation for SpRAM as a non-volatile memory that can achieve low power consumption and large capacity while maintaining the advantages of MRAM, which is high speed and the number of rewrites is almost infinite.
JP-A-10-116490 US Patent No. 20030072174 U.S. Patent No. 005695864 J. Nahas et al., IEEE / ISSCC 2004 Visulas Supplement p.22

In the already proposed SpRAM, data rewrite of “0” and “1” is performed by changing the polarity of the spin injection current.
However, because of the instability inherent in the spin transfer magnetization reversal phenomenon, the result of the magnetization reversal cannot always be determined only by the polarity of the spin injection current.
In SpRAM, in addition to the magnetization states corresponding to the data of “0” and “1”, there exists a metastable state that is established only when a spin injection current is passed. The instability of the magnetization reversal result is due to the phenomenon that the magnetization state after turning off the current becomes unstable once the magnetization is captured in the metastable state.

  The present invention provides a resistance change type memory device having a configuration capable of realizing stable magnetization reversal over a wide range of injection current.

  The resistance change type memory device according to the first aspect of the present invention includes a magnetic layer capable of reversal of magnetization in a resistance change type memory cell for writing data using a spin transfer effect by current injection. Including a tunnel magnetoresistive effect element stack formed on a conductive layer, and a line connecting the centers of the layers of the stack is oblique from a direction perpendicular to the surface of the conductive layer on which the stack is formed. The laminated body is formed at a tilt.

In a laminated body of tunnel magnetoresistive effect elements having such a structure, a current flows according to a voltage applied in the lamination direction (layer thickness direction). When a normal laminated body, that is, a line connecting the centers of the layers is parallel to the laminating direction, the direction of the flowing current substantially coincides with the laminating direction.
On the other hand, if the line connecting the centers of the layers is inclined obliquely from the direction perpendicular to the laminated surface (surface of the underlying conductive layer) as described above, the direction of the current vector is also inclined accordingly.
In such a configuration, when the current vector becomes oblique, an internal magnetic field that prevents the magnetization for storage from being directed in the direction in which the metastable state exists is generated due to the current component in a certain direction. In other words, when a current component having a specific direction with an oblique current vector is generated, there is an effect that the transition to the metastable state is prevented according to the magnitude of the current component.

  The resistance change type memory device according to the second aspect of the present invention includes a first conductive layer and a second conductive layer in a resistance change type memory cell that writes data using a spin transfer effect by current injection. A tunnel magnetoresistive element including a magnetic layer capable of reversing the magnetization formed between the layers, a contact surface between the stack and the first conductive layer, the stack and the second conductive layer. The contact surface of the layer is formed at a position shifted in the magnetization reversal direction.

In the resistance change type memory device according to the second aspect, the current vector is inclined as in the first aspect.
In particular, in the second aspect, the two contact surfaces serving as the current inlet and the outlet are arranged obliquely, whereby the current path distribution as a whole becomes oblique. Therefore, there is an effect that the transition to the metastable state is prevented due to a specific current component generated.

  In the first and second aspects, more preferably, in the stacked body, the cross-sectional areas of the stacked body portions other than the ferromagnetic tunnel structure are different on one side and the other side in the stacking direction of the ferromagnetic tunnel structure.

  According to the present invention, it is possible to provide a resistance change memory device having a configuration capable of realizing stable magnetization reversal over a wide range of injection current.

Embodiments of the present invention will be described below with reference to the drawings by taking SpRAM as an example.
Hereinafter, the cross-sectional element structure and phenomenon common to the first to third and more detailed embodiments to be described later will be described first.

<Cross-sectional element structure common to the embodiments>
FIG. 1 is a schematic cross-sectional view of an SpRAM memory cell MC that performs data inversion of “0” and “1” by a spin injection current in relation to a comparative example to which the present invention is not applied.
In the memory cell MC illustrated in FIG. 1, a tunnel magnetoresistive element 1 and a select element are connected in series between a bit line 32 made of an upper layer wiring and a source line (not shown).
The select element is an element that electrically selects a memory cell for reading or writing, and a diode, a MOS transistor, or the like can be used. FIG. 1 shows an example in which a MOS transistor (select transistor 41) is used as the select element.

On the Si substrate 40, a diffusion layer 42 and a diffusion layer 43 of the select transistor 41 are formed apart from each other across a region where a channel is formed. Impurities are introduced into the diffusion layer 42 and the diffusion layer 43 so as to be opposite in conductivity type to the region where the channel is formed, and the resistance is reduced. Among these, the diffusion layer 42 is connected to the source line at a location not shown.
The diffusion layer 43 is connected to one end (lower end) of the tunnel magnetoresistive effect element 1 through the connection plug 31.
The other end (upper end) of the tunnel magnetoresistive element 1 is connected to the bit line 32. The gate of the select transistor 41 has a laminated structure of a thin gate insulating film (not shown) and a gate conductive layer. The gate conductive layer functions as the selection signal line 30 or the conductive layer is connected to another selection signal line 30.

Tunneling magneto-resistance effect element 1 includes a storage layer 16 whose magnetization rotates relatively easily, and magnetization fixed layers 12 and 14.
The storage layer 16 and the magnetization fixed layers 12 and 14 are made of, for example, a ferromagnetic material mainly composed of nickel (Ni), iron (Fe), cobalt (Co), or an alloy thereof.
The storage layer 16 may be composed of a plurality of magnetic layers, and these may be collectively referred to as the free layer 3. In the example illustrated in FIG. 1, the free layer 3 includes a tunnel barrier layer 15, a storage layer 16, and a nonmagnetic layer 17 in order from the lower layer.

  The magnetization fixed layer 12 and the magnetization fixed layer 14 are antiferromagnetically coupled via the nonmagnetic layer 13, and the magnetization fixed layer 12 is formed in contact with the antiferromagnetic material 11. Although there is a strong unidirectional magnetic anisotropy due to exchange interaction acting between these layers, these may be collectively referred to as a fixed layer 2. In the example illustrated in FIG. 1, the fixed layer 2 includes a base film 10, an antiferromagnetic material 11, a magnetization fixed layer 12, a nonmagnetic layer 13, and a magnetization fixed layer 14 in order from the lower layer.

As a material for the nonmagnetic layer 13 and the nonmagnetic layer 17, tantalum (Ta), copper (Cr), ruthenium (Ru), or the like can be used. Due to strong antiferromagnetic coupling through the nonmagnetic layer 13 in a steady state, the magnetization 51 of the magnetization fixed layer 12 and the magnetization (hereinafter referred to as reference layer magnetization) 52 of the magnetization fixed layer 14 are in a substantially complete antiparallel state.
Normally, the saturation magnetization film thickness products of the magnetization fixed layer 12 and the magnetization fixed layer 14 are equal, and the leakage component of the magnetic pole magnetic field is negligibly small.
Examples of antiferromagnetic materials include manganese alloys such as iron (Fe), nickel (Ni), platinum (Pt), iridium (Ir), and rhodium (Rh), cobalt (Co), and nickel oxide. it can.

  In addition, a tunnel barrier layer 15 made of an insulating layer made of an oxide layer such as aluminum (Al), magnesium (Mg), silicon (Si), or nitride is disposed between the storage layer 16 and the fixed magnetization layer 14. It has been. The tunnel barrier layer 15 plays a role of cutting the magnetic coupling between the storage layer 16 and the magnetization fixed layer 14 and flowing a tunnel current.

  These magnetic films and conductor films are mainly formed by sputtering, and the tunnel barrier layer can be obtained by oxidizing or nitriding a metal film formed by sputtering.

The nonmagnetic layer 17 is a topcoat film, and plays a role of preventing mutual diffusion between the tunnel magnetoresistive effect element and the wiring connecting the tunnel magnetoresistive effect element, reducing contact resistance, and preventing the memory layer 16 from being oxidized. For the top coat film, materials such as copper (Cu), tantalum (Ta), and titanium nitride can be usually used.
The base film 10 has an effect of increasing the crystallinity of the film stacked above the base film. As the material of the base film 10, chromium (Cr), tantalum (Ta), or the like can be used.

The state of the memory cell can be determined based on whether the magnetization of the storage layer 16 (hereinafter referred to as storage layer magnetization) 53 and the magnetization of the fixed magnetization layer 14 (reference layer magnetization) 52 are in a parallel state or antiparallel state. .
In order to read or rewrite the state of the memory cell, it is necessary to pass a spin injection current 70.
The spin injection current 70 passes through the diffusion layer 43, the tunnel magnetoresistive element 1 and the bit line 32.

FIG. 2 shows an example of an apparatus for measuring SpRAM characteristics.
It is possible to invert the data 53 of the free layer of the tunnel magnetoresistive effect element 1 between “0” and “1” by the bias current magnetic field 72 in addition to the spin injection current 70.
A state diagram of a memory cell in which the pulse peak value of the spin injection current 70 is plotted on the vertical axis and the pulse peak value of the bias current magnetic field 72 is plotted on the horizontal axis is referred to as a phase diagram.
The apparatus illustrated in FIG. 2 uses a Helmholtz coil 74 to generate a bias current magnetic field 72. The bias current 71 flowing through the Helmholtz coil 74 is supplied independently from the external power source 73. The spin injection current 70 flows in or out from another driving circuit via the bit line 32 connected to the memory cell.
If the apparatus of FIG. 2 is used, the magnitude | size and phase of the spin injection current 70 and the bias current magnetic field 72 can be set arbitrarily, and the measurement for creating a phase diagram can be performed.

FIG. 3 is a diagram illustrating the timing of applying the pulse of the spin injection current 70 and the pulse of the bias current 71.
The initial state is shown by the code _{t 0.} For simplicity, both the spin injection current 70 and the bias current 71 are rectangular pulses.
The rise times of the spin injection current 70 and the bias current 71 are indicated by symbols t ₁ and t ₂ , respectively. The fall times of the spin injection current 70 and the bias current 71 are indicated by symbols t ₃ and t ₄ , respectively.
At time t ₅ , the resistance state determined by the angle formed by the storage layer magnetization 53 and the reference layer magnetization 52 is read to determine the end state.

FIG. 4 is a memory cell state diagram in the pulse duration 10 [ns] of the SpRAM to which the present invention is not applied. The memory cell state diagram shows the correlation between the spin injection current value and the cell state, with the pulse peak value of the spin injection current 70 on the vertical axis and the memory cell address on the horizontal axis.
The initial state before flowing the spin injection current is aligned so that, for example, the storage layer magnetization 53 and the reference layer magnetization 52 are in an antiparallel state depending on the polarity of the bias current magnetic field 72.

The cell state shown in the memory cell state diagram is a state finally reached as a result of magnetization reversal.
In MRAM including SpRAM, it is preferable that there are two unstable magnetization states in which data storage of “0” and “1” is obvious, and there is an unstable region where data storage of “0” and “1” is not clear. Absent.
When there is no spin transfer torque, for example, in an MRAM to which the present invention is not applied, a stable magnetization state corresponds to a potential energy valley of the storage layer magnetization 53.

<Description of phenomena common to the embodiments>
According to the following document 1 ^{(* 1)} , the torque from the effective magnetic field acting on the storage layer magnetization is expressed by the following equation (1).
(* 1) Reference 1: “MR Gibbons,“ Micromagnetic Simulation using the dynamic alternating direction implicit method ”, J. Magn. Magn. Mater., 186, pp.389 (1998)”

  The effective magnetic field is the potential energy of storage layer magnetization,

となる関係にある。

It is in a relationship.

  The potential energy is further expressed by the following equation (3).

メモリ素子が図２のような装置内置かれた場合、外部磁界は注入電流磁界とバイアス電流磁界の和になる。

When the memory element is placed in the apparatus as shown in FIG. 2, the external magnetic field is the sum of the injected current magnetic field and the bias current magnetic field.

  In the element structure as shown in FIG. 1, since the magnetic field induced by the current flowing through the tunnel magnetoresistive effect element 1 and the connection plug 31 is a vortex magnetic field, there is no effect of directing the storage layer magnetization in a uniform direction. .

  As described in the patent document (Japanese Patent Laid-Open No. 2005-277147), there is already an invention in which a magnetic field induced by an injection current flowing through the bit line 32 acts on the storage layer magnetization.

Torque from the effective magnetic field acts until the final state of the system converges to a potential energy valley. If the storage layer magnetization is in a uniform magnetization state, the potential energy valleys are a state in which the storage layer magnetization 53 and the reference layer magnetization 52 are parallel, and a state in which the storage layer magnetization 53 and the reference layer magnetization 52 are antiparallel. It is known that there are two.
Therefore, by applying a current magnetic field or the like from the outside, the initial state can be shifted to an energetically unstable state, and the end state can be reduced to a state opposite to the initial state.

  However, in the case of SpRAM, in addition to the magnetization state corresponding to the data of “0” and “1”, there exists a metastable state that is established only when a spin injection current is passed, and the magnetization is once trapped in the metastable state. In rare cases, the magnetization state after turning off the current may become indefinite.

According to Document 2 ^{(* 2)} below, torque (spin transfer torque) transmitted from spin-polarized electrons is expressed by the following equation (4).
(* 2) Reference 2: “YB Bazaliy, et.al.,“ Modification of the Landau-Lifshitz equation in the presence of a spin-polarized current in Colossal- and giant-Magnetoresistive Materials ”, PRB 57, pp.R3213 ( 1998) ''

となる関係にある。

It is in a relationship.

  The kinetic energy of conduction electrons is further expressed by the following formula (6).

As shown in FIG. 1, when the injection current density vector is oriented in a direction perpendicular to the planar surface (Jx = Jy = 0, Jz ≠ 0), the kinetic energy valley of the conduction electrons is also perpendicular to the planar surface. It will turn.
The valley of the kinetic energy can be regarded as a metastable state because it is stable only when an injection current is passed.
In SpRAM, the kinetic energy valleys of conduction electrons are oriented in a different direction from the magnetization potential energy valleys. For this reason, once captured in the metastable state during the transition, the end state rarely becomes independent of the initial state.
The unstable region 76 shown in FIG. 4 reflects that the magnetization was trapped in a metastable state in the course of transition.

FIG. 5A is a schematic diagram showing a magnetization transition process when magnetization reversal is normally performed.
It is assumed that the storage layer magnetization 53 is in the + x direction and the reference layer magnetization 52 is in the −x direction in the initial state. When a spin injection current 70 of a threshold value or more is passed, the magnetization is reversed in the −x direction over time while precessing around the x axis. This is the case where there are two stable states, the anti-parallel state (0 state) and the parallel state (1 state), and it is possible to switch from one state to another state by passing a current of threshold current 75 or more. Represents.

FIG. 5B is a schematic diagram showing a magnetization transition process when the magnetization reversal is not normally performed.
It is assumed that the storage layer magnetization 53 is in the + x direction and the reference layer magnetization 52 is in the −x direction in the initial state. When a spin injection current 70 exceeding the threshold is applied, the magnetization precesses around the x axis, but it changes to precession around the z axis. This is because precession around the z-axis is established as a metastable state. This phenomenon rarely occurs when the kinetic energy of conduction electrons exceeds the potential energy of magnetization.

The metastable state can exist only in a state where the conduction electrons have obtained kinetic energy, that is, within the time during which the spin injection current 70 flows. Therefore, the state after the current flow is stopped can reach either “0” or “1”.
FIG. 5B shows that the state after turning off the current has returned to the initial magnetization state because the magnetization was trapped in the metastable state during switching.

The phenomenon that the magnetization state becomes unstable as described above deteriorates the reliability of data writing in the SpRAM.
Although some error in writing can be saved by the error correction circuit, in that case, the chip area and power consumption increase due to the extra circuit.
Further, as long as such an unstable phenomenon exists, it becomes difficult to use the SpRAM as the main memory. Then, the result is that the value of SpRAM as a nonvolatile memory for improving the performance of the data device is extremely low.

<< First Embodiment >>
The reason why the switching end state transits to a state different from the intended state in the SpRAM is that the metastable state temporarily generated by passing the spin injection current 70 disturbs the intended transition trajectory.
With the structure as shown in FIG. 1, it is difficult to completely prevent the metastable state from being temporarily induced as long as the principle of spin transfer magnetization rotation is used.
However, if the direction in which the metastable state exists (the z-axis direction in FIG. 5B) is known, the direction in which the spin injection current flows is optimized so that the storage layer magnetization 53 does not face that direction. It is possible.

伝導電子の運動エネルギーの谷がプレーナ面（厳密には、トンネル磁気抵抗効果素子１が形成された接続プラグ３１の上面）に対して垂直以外の方向を向くと、記憶層磁化５３が垂直方向を向いて準安定状態をとる確率を大幅に低減できる。ここで、電流密度ベクトルにプレーナ面と平行な電流ベクトル成分（または）のうち、磁化の反転方向であるｘ方向と直交する方向の電流ベクトル成分（ここでは、図６では電流成分Ｉ_ｙにより表記）が大きくなると、より準安定状態をとる確率が減少するため望ましい。準安定状態をとる確率が減少すれば、磁化遷移結果が不定になることもなくなり、不安定領域は解消される。
詳しい検討に依れば、プレーナ面と平行な面（本例では接続プラグ３１の上面）に対して、トンネル磁気抵抗効果素子１および接続プラグ３１を傾斜させる角度７７は５度〜８５度の範囲にあるのが望ましい。 FIG. 6 is a schematic cross-sectional view of the SpRAM according to the first embodiment.

When the valley of the kinetic energy of the conduction electrons faces a direction other than perpendicular to the planar surface (strictly speaking, the upper surface of the connection plug 31 on which the tunnel magnetoresistive element 1 is formed), the storage layer magnetization 53 becomes perpendicular. The probability of facing and taking a metastable state can be greatly reduced. Here, among the current vector components (or) parallel to the planar surface in the current density vector, the current vector component in the direction orthogonal to the x direction, which is the magnetization reversal direction (here, represented by the current component I _{y in} FIG. 6). ) Increases, the probability of taking a metastable state decreases, which is desirable. If the probability of the metastable state is reduced, the magnetization transition result will not be indefinite, and the unstable region is eliminated.
According to a detailed study, the angle 77 for inclining the tunnel magnetoresistive effect element 1 and the connection plug 31 with respect to a plane parallel to the planar surface (in this example, the upper surface of the connection plug 31) is in the range of 5 to 85 degrees. It is desirable to be in

FIG. 7 is a schematic diagram illustrating a magnetization transition process when magnetization reversal is normally performed in the first embodiment.
It is assumed that the storage layer magnetization 53 is in the + x direction and the reference layer magnetization 52 is in the −x direction in the initial state. By tilting the tunnel magnetoresistive effect element 1 and the connection plug 31, the storage layer magnetization 53 ends the transition without being directed in the direction in which the metastable state exists.

FIG. 8 is a memory cell state diagram when the total of the current pulse train duration and the standby time is 10 [ns] in the first embodiment.
The memory cell state diagram is drawn with the crest value of the current pulse train as the vertical axis and the address of the memory cell as the horizontal axis.

The angle 77 for inclining the tunnel magnetoresistive effect element 1 and the connection plug 31 is approximately 30 degrees. At this time, by moving the valley of the kinetic energy, the state where the inversion result as seen in FIG.
As a secondary effect of tilting the tunnel magnetoresistive effect element 1 and the connection plug 31, a current magnetic field induced by the spin injection current 70 flowing through the tunnel magnetoresistive effect element 1 and the connection plug 31 is applied to the storage layer magnetization 53. Can act. In order to enhance this effect, it is preferable to adjust the cross-sectional area so as to provide a difference between the current density before passing through the tunnel magnetoresistive effect element 1 and the current after passing.

In order to obtain the structure shown in FIG. 6, for example, an oblique hole is formed in the buried insulating film by oblique etching, and a plug material is buried in this hole to form the connection plug 31. Next, each film constituting the tunnel magnetoresistive effect element 1 is formed so as to be in contact with the upper surface of the connection plug 31 on the buried insulating film.
Thereafter, a mask layer such as a resist is formed, and the respective films constituting the tunnel magnetoresistive effect element 1 around the mask layer are sequentially removed by oblique etching.
When the mask layer is removed, the formation of the laminated body of the oblique connection plug 31 and the tunnel magnetoresistive effect element 1 in FIG. 6 is completed. Other transistors and wirings are formed according to a normal method.

Here, FIG. 6 illustrates an in-plane magnetization type MTJ.
In the present embodiment, the direction of the easy magnetization axis is the “magnetization reversal direction”, and this direction corresponds to the direction of the x-axis 91 here.
The “direction perpendicular to the magnetization reversal direction” corresponds to the direction of the y-axis 92.
The reference (in the direction of zero inclination) when “the line connecting the centers of the layers of the laminated body constituting the tunnel magnetoresistive effect element 1 is inclined” is perpendicular to the upper surface of the connection plug 31 (the surface on which the laminated body is formed). This is the direction of the x-axis 93.

In the in-plane magnetization type MTJ shown in FIG. 6, the tunnel magnetoresistive effect element 1 is configured such that the planar shape of each layer constituting the MTJ is magnetized in the direction of easy magnetization (direction of easy axis of magnetization) and in the plane of the magnetic layer. It is desirable that the dimensions are different in the direction perpendicular to the direction of the easy axis. For this reason, in FIG. 6, for example, the planar shape of each layer constituting the MTJ is an ellipse.
More specifically, in FIG. 6, one of the prescriptions for the ease of magnetization is an elliptical planar shape, and the magnetization is easily stabilized in the major axis direction of the ellipse (the direction of the x-axis 91). Conversely, the magnetization is not stable in the minor axis direction of the ellipse (the direction of the y-axis 92). Therefore, the magnetization reversal direction is set to the x-axis 91 direction.

<< Second Embodiment >>
The reason why the switching end state transits to a state different from the intended state in the SpRAM is that the metastable state temporarily generated by passing the spin injection current 70 disturbs the intended transition trajectory.
With the structure as shown in FIG. 1, it is difficult to completely prevent the metastable state from being temporarily induced as long as the principle of spin transfer magnetization rotation is used. However, if the direction in which the metastable state exists (the z-axis direction in FIG. 5B) is known, the stacking direction of the tunnel magnetoresistive effect element 1 is optimized so that the storage layer magnetization 53 does not face that direction. It is possible to

伝導電子の運動エネルギーの谷がプレーナ面（厳密には、トンネル磁気抵抗効果素子１が形成された接続プラグ３１の上面）に対して垂直以外の方向を向くと、記憶層磁化５３が垂直方向を向いて準安定状態をとる確率を大幅に低減できる。準安定状態をとる確率が減少すれば、磁化遷移結果が不定になることもなくなり、不安定領域は解消される。
詳しい検討に依れば、プレーナ面と平行な面（本例では接続プラグ３１の上面）に対して、トンネル磁気抵抗効果素子１および接続プラグ３１を傾斜させる角度７７は５度〜８５度の範囲にあるのが望ましい。 FIG. 9 is a schematic cross-sectional view of an SpRAM according to the second embodiment.

When the valley of the kinetic energy of the conduction electrons faces a direction other than perpendicular to the planar surface (strictly speaking, the upper surface of the connection plug 31 on which the tunnel magnetoresistive element 1 is formed), the storage layer magnetization 53 becomes perpendicular. The probability of facing and taking a metastable state can be greatly reduced. If the probability of the metastable state is reduced, the magnetization transition result will not be indefinite, and the unstable region is eliminated.
According to a detailed study, the angle 77 for inclining the tunnel magnetoresistive effect element 1 and the connection plug 31 with respect to a plane parallel to the planar surface (in this example, the upper surface of the connection plug 31) is in the range of 5 to 85 degrees. It is desirable to be in

The magnetization transition process in the case where the magnetization reversal was normally performed was substantially the same as the schematic diagram related to the first embodiment shown in FIG.
In FIG. 7, it is assumed that the storage layer magnetization 53 is in the + x direction and the reference layer magnetization 52 is in the −x direction in the initial state.
By tilting the plane formed by the tunnel magnetoresistive effect element 1, the storage layer magnetization 53 ends the transition without facing the direction in which the metastable state exists.

Further, the same memory cell state diagram as that of the first embodiment of FIG. 8 was obtained when the sum of the current pulse train duration and the standby time was 10 [ns].
In FIG. 8, the memory cell state diagram is drawn with the crest value of the current pulse train as the vertical axis and the address of the memory cell as the horizontal axis. The angle 77 for tilting the tunnel magnetoresistive element 1 is approximately 30 degrees.

By moving the valley of the kinetic energy, it was possible to completely eliminate the state in which the inversion result was indefinite as seen in FIG.
As a secondary effect of tilting the tunnel magnetoresistive effect element 1, a current magnetic field induced by the spin injection current 70 flowing through the tunnel magnetoresistive effect element 1 can be applied to the storage layer magnetization 53. In order to enhance this effect, it is preferable to adjust the cross-sectional area so as to provide a difference between the current density before passing through the tunnel magnetoresistive effect element 1 and the current after passing.

  As shown in FIG. 9, it is necessary to form the tunnel magnetoresistive element 1 so that each layer is inclined with respect to the upper surface of the connection plug 31 substantially parallel to the planar surface. For this purpose, when the oblique etching described in the first embodiment is used, the oblique tunnel magnetoresistive effect element 1 shown in FIG. 6 is formed on the upper surface of the straight connection plug 31. Although such a form may be sufficient, in order to make it like FIG. 9, the following method can be employ | adopted, for example.

Even when the lower surface in contact with the upper surface of the connection plug 31 is horizontal, the upper surface of the base film 10 is formed obliquely from the horizontal plane.
As a method for processing such a base film 10, for example, the amount of transmitted light gradually decreases from one to the other with respect to a transfer plane of a certain pattern by a device on a photomask.

When such a devised photomask is used, the cross-sectional shape of the resist after exposure becomes a shape in which only the upper surface is slanted like the base film 10 in FIG. When this resist is etched back under a condition with a low selectivity to the base film material to some extent, the base film is gradually deeply etched from one to the other in the process of removing the resist. Finally, patterning is performed like the base film 10 reflecting the resist shape.
Thereafter, when the other constituent films of the fixed layer 2 and the constituent films of the free layer 3 are sequentially formed on the base film 10 and patterned, the tunnel magnetoresistive effect element 1 as shown in FIG. 9 can be realized.

<< Third Embodiment >>
As shown in FIG. 10, before forming the tunnel magnetoresistive effect element 1, a conductive contact layer 33 and a surrounding insulating layer 34 are formed on the upper surface of the connection plug 31 to limit the current path. Then, the tunnel magnetoresistive element 1 is formed obliquely on the insulating layer 34 in which the conductive contact layer 33 is embedded by the above-described manufacturing method.
Here, the direction in which the tunnel magnetoresistive effect element 1 is inclined is indicated by a symbol “A” in FIG. 10, and the direction opposite to the direction A is indicated by a symbol “B”.

As shown in FIG. 10, the tunnel magnetoresistive effect element 1 is formed on the conductive contact layer 33 so that the conductive contact layer 33 is in contact with the lower surface of the tunnel magnetoresistive effect element 1 at a position near the direction B.
Next, the bit line 32 is formed. At that time, the bit line 32 is narrower than the upper surface of the tunnel magnetoresistive element 1 so as to limit the current path to the uppermost film of the planarizing film in which the tunnel magnetoresistive element 1 is embedded. Opening 35 is formed. Then, the bit line 32 is electrically connected to the tunnel magnetoresistive element 1 through the opening 35.
The position of the opening 35 is a position near the direction B opposite to the direction A in which the tunnel magnetoresistive element 1 is inclined. For this reason, the average direction of the current is defined by the conductive contact layer 33 and the opening 35 and becomes oblique.

The arrangement of the conductive contact layer 33 and the opening 35 enhances the effect of forming the tunnel magnetoresistive element 1 obliquely, that is, the effect of obstructing the transition to the metastable state. For this reason, a memory with a lower error rate can be realized.
If the effect is sufficient due to the arrangement of the conductive contact layer 33 and the opening 35, the tunnel magnetoresistive element 1 does not necessarily need to be inclined. Such a form is also included in the third embodiment. Further, shifting the arrangement of the conductive contact layer 33 and the opening 35 can be applied to the second embodiment.

<< 4th Embodiment >>
As shown in FIG. 11, the effects of the first embodiment can be obtained even if the cross-sectional areas of the magnetization fixed layer 14, the tunnel barrier layer 15, and the storage layer 16 having the MTJ structure are changed on one side and the other side in the stacking direction. The effect of enhancing is obtained.
This is because the current component that generates the internal magnetic field in the direction that prevents the transition to the metastable state is generated in a magnitude proportional to the cross-sectional area. That is, the greater the current component is above and below the unbalanced MTJ structure, the greater the strength of the internal magnetic field that prevents the transition to the metastable state.

Formation of a laminated body having different cross-sectional areas is achieved by forming the tunnel magnetoresistive effect element 1 in two etchings with different processing pattern sizes.
The assist effect that prevents the transition to the metastable state by changing the cross-sectional area is based on the presence of a current component that generates an internal magnetic field that prevents the transition to the metastable state. For this reason, changing the cross-sectional area alone has no effect, and the effect is exhibited in the form of the fourth embodiment combined with the first or second embodiment. Furthermore, the present invention can be applied to the third embodiment and further combined with any other embodiment.

  In the first to fourth embodiments described above, a tunnel magnetoresistive element having an in-plane magnetization type MTJ is taken as an example. However, it is also possible to change to a perpendicular magneto-resistance type, that is, a tunnel magnetoresistive effect element in the perpendicular direction (normal direction) of each layer of the multilayer body constituting the MTJ. Even in this case, “the line connecting the centers of the layers of the laminate is inclined obliquely from the direction perpendicular to the surface of the conductive layer on which the laminate is formed (based on the perpendicular direction)”. There is no. However, the magnetization facilitating direction (the facilitating axis direction) is the x-axis 93, and when the MTJ laminate is tilted obliquely in a direction orthogonal to the facilitating axis direction, for example, the y-axis 92 side, the above-described Similarly to the in-plane magnetization type, the effect that the transition probability to the metastable state is reduced can be obtained.

  According to the first to fourth embodiments described above in detail, the instability associated with the spin transfer magnetization reversal is removed, and the data of the memory cell can be reversed with high reliability “0” and “1”. As a result, it becomes easy to reduce the size, increase the reliability, increase the capacity, and reduce the power consumption of the SpRAM.

It is a cross-sectional schematic diagram of the memory cell of SpRAM in connection with a comparative example. It is a figure which shows the apparatus which measures the characteristic of SpRAM which can be used by embodiment. FIG. 4 is a timing chart for applying each pulse of a spin injection current and a bias current in the measurement in the embodiment. It is a memory cell state figure in pulse duration 10 [ns] regarding SpRAM of a comparative example. (A) is a figure when a magnetization reversal is performed normally, (B) is a figure which shows the magnetization transition process when a magnetization reversal is not performed normally. It is a cross-sectional schematic diagram of SpRAM in connection with 1st Embodiment. It is a schematic diagram which shows the magnetization transition process when magnetization reversal is performed normally in 1st Embodiment. FIG. 6 is a memory cell state diagram when the sum of the current pulse train duration and the standby time is 10 [ns] in the first embodiment. It is a cross-sectional schematic diagram of SpRAM in connection with 2nd Embodiment. It is a cross-sectional schematic diagram of SpRAM in connection with 3rd Embodiment. It is a cross-sectional schematic diagram of SpRAM in connection with 4th Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Tunnel magnetoresistive effect element, 2 ... Fixed layer, 3 ... Free layer, 10 ... Underlayer, 11 ... Antiferromagnetic material, 12 ... Magnetization fixed layer, 13 ... Nonmagnetic layer, 14 ... Magnetization fixed layer, 15 ... Tunnel barrier layer, 16 ... storage layer, 17 ... nonmagnetic layer, 30 ... selection signal line, 31 ... connection plug, 32 ... bit line, 33 ... conductive contact layer, 34 ... insulating layer, 35 ... opening, 41 ... select Transistor, 51, 52, 53 ... Magnetization, MC ... Memory cell

Claims (8)

A stack of tunnel magnetoresistive elements formed on a conductive layer, including a magnetic layer whose magnetization direction can be reversed, in a resistance change type memory cell that writes data using a spin transfer effect by current injection. Have a body,
A resistance change type memory device in which a line connecting the centers of the layers of the stacked body is inclined from a direction perpendicular to a surface of the conductive layer on which the stacked body is formed, thereby forming the stacked body. A line connecting the centers of the layers of the laminate is inclined at an angle within a range of 5 degrees or more and 85 degrees or less from a direction perpendicular to the surface of the conductive layer on which the laminate is formed, thereby forming the laminate. The resistance change type memory device according to claim 1. A line connecting the centers of the layers of the laminate is inclined obliquely from a direction perpendicular to the surface of the conductive layer on which the laminate is formed to a direction perpendicular to the magnetization reversal direction, thereby forming the laminate. The resistance change type memory device according to claim 1. The laminate is formed between a first conductive layer and a second conductive layer;
The contact surface between the stacked body and the first conductive layer and the contact surface between the stacked body and the second conductive layer are formed at positions shifted in a direction orthogonal to the magnetization reversal direction. 2. The resistance change type memory device according to 1. The laminate includes a ferromagnetic tunnel structure formed of an insulating layer and two ferromagnetic layers sandwiching the insulating layer,
The resistance change type memory device according to claim 1, wherein the stacked body has different cross-sectional areas of a stacked body portion other than the ferromagnetic tunnel structure on one side and the other side in the stacking direction of the ferromagnetic tunnel structure. The cross-sectional area of the laminated body portion on the side where current is injected into the ferromagnetic tunnel structure is smaller than the cross-sectional area of the laminated body portion where current flows out of the ferromagnetic tunnel structure. The resistance change type memory device described. A resistance change type memory cell for writing data using a spin transfer effect by current injection includes a magnetic layer formed between the first conductive layer and the second conductive layer and capable of reversing the magnetization. Having a stack of tunnel magnetoresistive elements,
The contact surface between the stacked body and the first conductive layer and the contact surface between the stacked body and the second conductive layer are formed at positions shifted in a direction orthogonal to the magnetization reversal direction. Type memory device. The cross-sectional area of the laminate portion on the side where current is injected into the ferromagnetic tunnel structure is smaller than the cross-sectional area of the laminate portion on the side where current flows out of the ferromagnetic tunnel structure. The resistance change type memory device described.

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